Hrbek



March 10, 1964 G. w. H'RBEK 3,124,756

EXTREMELY HIGH FREQUENCY PUMP FOR ELECTRON BEAM PARAMETRIC AMPLIFIER Filed Sept. ll. 1961 2 Sheets-Sheet 1 INVENTOR.

George W HreK March 10, 1964 G w HRBEK 3,124,756

EXTREMELY HIGH EREQ'MENCY PUMP FOR ELECTRON BEAM PARAMETRIC AMPLIFIER Filed Sept. 11, 1961 2 Sheets-Sheet 2 IN VENTOR.

George W' Hrbeifl 0% fig.

United States Patent 3,124,756 EXTREMELY HIGH FREQUENCY PUMP FOR ELECTRON BEAM PARAMETRIC AMPLIFIER George W. Hrbek, Elk Grove Village, Ill., assignor to Zenith Radio Corporation, a corporation of Delaware Filed Sept. 11, 1961, Ser. No. 137,108 8 Claims. (Cl. 330--4.7)

The present application pertains to parametric amplifiers It is particularly directed to electron beam devices employing a parametric gain producing mechanism.

Various forms of the electron beam parametric amplifier have been disclosed to the art and have attracted much attention because of the versatility of their application and particularly because of their ability to yield high gain with very good signal-to-noise ratios. However, the specific forms of amplifier presently in use encounter practical construction difficulties as they are adapted to higher and higher frequencies. This situation is aggravated in certain applications where it is desirable in the interest of noise reduction to utilize a parametric pumping mechanism which must exhibit a wave transmission velocity having a finite value.

It is accordingly an object of the present invention to provide an electron beam parametric amplifier capable of overcoming the aforenoted difliculties.

Another object of the present invention is to provide an electron beam parametric amplifier capable of operating at extremely high frequencies.

A further object of the present invention is to provide a new and improved high frequency amplifier of the kind described which may be constructed with reasonable and practicable dimensions and tolerances.

An amplifier constructed in accordance with the present invention includes means for projecting a first electron beam along a first path together with means for establishing resonance of the electrons in the beam. An input coupler develops on the beam a wave, corresponding to input signal energy, having a predetermined frequency and propagation constant. The amplifier also includes means for projecting at least one additional electron beam along a second path disposed in field coupling relationship with the first beam. Cooperating with the additional beam are means for developing thereon a pump signal wave having a frequency and propagation constant selected with respect to these characteristics of the input signal wave to subject the electrons in the first beam to a time variable periodic in homogeneous field having a phase relationship with the first beam wave to deliver energy to a component thereof in proportion to the amplitude of that component. Finally, there is included means for extracting signal energy from the first electron beam.

The features of the present invention which are believed to be novel are set forth with particularity in the appended claims. The organization and manner of operation of the invention, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like numerals identify like elements, and in which:

FIGURE 1 is a schematic representation of a parametric amplifier constructed in accordance with one embodiment of the present invention;

FIGURE 1a is a fragmentary cross-sectional view of an alternate component which may be employed in the apparatus illustrated in FIGURE 1;

FIGURE 2 is a schematic representation of another embodiment of the present invention;

FIGURE 3 is a schematic representation of a still further embodiment of the present invention; and

FIGURE 3a is a fragmentary cross-sectional view,

3,124,756 Patented Mar. 10, 1964 2 partially in schematic form, as if taken along lines 3a3a in FIGURE 3.

The parametric amplifier illustrated in FIGURE 1 includes an electron gun 10 which projects an electron beam along a primary path 11 which terminates in a collector electrode 12 connected to a suitable source of potential B+. Gun 10 is conventional and as schematically illustrated is of the usual Pierce type construction including a cathode and suitable beam forming electrodes to develop a pencil-like electron stream preferably having the characteristics of Brillouin flow.

The electron beam projected along path 11 is subjected to a force establishing resonance of the beam electrons at an assigned frequency. In the present instance, the resonance suspension is created by an axial magnetic field indicated by arrow H which may be conveniently developed by immersing the entire device in a solenoid.

Input signal energy to be amplified is impressed upon the electron beam from gun 10 by an electron coupler 13. In the present case, in which the magnetic field establishes for the electrons a resonant cyclotron frequency, coupler 13 may be of any suitable form to impart transverse electron motion representative of the input signal energy. Known couplers include various beam interaction devices and it is most convenient in the present instance to provide a pair of simple deflectors 14 disposed on opposite sides of beam path 10 and across which an input signal source 15 is coupled by means of an impedance matching transformer 16. In response tothe signal energy from source 15 and the conjoint influence of the magnetic field, the electrons in the beam are caused to follow expanding helical orbits the periods of which are determined by the magnetic field and the radii of which are determined by the input signal energy.

Disposed along beam path 11 downstream from input coupler 13 is an output coupler 18 constructed to interact with the electron beam at the frequency of the signal which is to be amplified. As illustrated, coupler 18 is identical in form to coupler 13, including a pair of deflectors 19 coupled to a load 20 by means of a matching transformer 21. The action in output coupler 18 is the reverse of that described with respect to coupler 13. That is, electrons following helical orbits deliver energy to the coupler and in so doing spiral inwardly toward the beam path, after which the electrons are intercepted by collector 12.

To amplify the signal energy modulated onto the electron stream by coupler 13, a parametric expander section is disposed along beam path 11 between the input and output couplers. This expander is in a form capable of developing high level pumping fields even at extremely high frequencies. To this end, the apparatus in FIGURE 1 includes four additional electron beams projected along individual paths 23, 24, and 26 circumferentially spaced symmetrically around the primary signal carrying beam path 11. For each of these additional beam paths, an electron gun 28, in this case structurally similar to electron gun It), is disposed on the respective beam path.

The invention contemplates developing on each of the additional beams a pump signal wave having a frequency and propagation constant selected with respect to the frequency and propagation constant of the input signal wave applied by coupler 13 so as to subject the electrons in the primary signal carrying beam to a time-variable inhomogeneous field having a phase relationship with the signal carrying wave to deliver energy to signal motion components thereof in linear proportion of the amplitude of the latter. To this end, the inhomogeneous field is produced by space-charge waves caused to propagate along each of the four additional electron beams. These waves conveniently are developed by modulating each of i? the additional beams with pump signal energy developed by a pumping source 30. As illustrated in FIGURE 1, the pump signal energy is caused to longitudinally modulate the additional beams by means of helices 31, anindividual one of which is disposed in interacting relationship with each of the four additional beams.

From a practical standpoint, it is convenient to dispose helices 31 circumferentially around input coupler 13 and to position electron guns 28 but a short distance ahead of the helices. This permits an increase in the length of the amplification region, between helices 31 and output coupler 18 without an increase in the overall length of the device. Similarly, the length of the additional beam paths 23-26 desirably is shortened by the provision of a separate annular collector electrode disposed just beyond helices 31. However, for ease of illustration in FIG- URE l, helices 31 are shown positioned along beam path 11 beyond electron coupler 13. In this form, unwanted direct coupling between helices 31 and the electron beam is avoided by enclosing the latter within a cylinder 32 coaxially enclosing electron beam path 11.

In order to obtain parametric action between the longitudinal-mode field developed upon the additional beams and the input signal wave carried by the primary beam, it is necessary that the pumping fields be inhomogeneous since it is such a time-varying electrostatic potential which imparts the energy delivering forces to the moving electrons. While only one additional beam is necessary to produce the pumping field, for reasons of symmetry at least two beams are desired and the preferred arrangement is that which employs four beams as illustrated so as to produce a quadrupole shaped pumping field. In correspondence therewith, the two pairs of oppositely disposed ones of helices 31 are coupled at one end to opposite ends of a push-pull source of pump signal energy established by the provision of a secondary winding on a secondary transformer 33 coupled to pump source 30. The other ends of helices 31 preferably are terminated in a resistor 34 to prevent reflection.

In operation, the space charge waves which propagate along the additional beam paths 23-26 beyond cylinder 32 conjointly develop the inhomogeneous timevarying field which is effective to deliver energy to the signal-modulated cyclotron wave developed by coupler 13 and thereby amplify the electron signal motion to which output coupler 18 subsequently responds. Details of the particular manner in which the quadrupole type of field amplifies the signal energy are contained in the copending application of Glen Wade, Serial No. 747,764,

filed July 10, 1958 and assigned to the same assignee as is the present application. This explanation also is detailed in an article by Adler et al. entitled A Low-Noise Electron-Beam Parametric Amplifier appearing in the Proceedings of the IRE, Volume 46, Number 10, for October 1958.

It is sufiicient therefore to note that either the fast or slow space charge waves may be utilized on the pumping beams and, similarly, either the fast or slow cyclotron waves on the beam may be amplified. It is merely necessary to make adjustments in the propagation velocities involved in order that the sum of the propagation constants of the input signal wave, the pump signal wave, and the inherently developed idler wave be equal to zero. The idler wave has a frequency equal to the difference between the pump and input signal frequencies. Of course, as is well understood, it is necessary in considering the frequency of the space charge waves developed upon the additional beams to consider the apparent reduction in frequency inherent to longitudinal-mode modulation and therefore to employ the reduced plasma frequency of the space charge waves in assigning the various constants. These factors will become more clear in connection with the discussion below of the apparatus illustrated in FIGURE 2.

As in the case of couplers 13, 18, various known mechanisms may be employed to velocity-modulate the additional electron beams; for example, the double-gap cavity shown in FIGURE 1a is of a type which has heretofore been used in electron beam apparatus for impressing signal energy upon or deriving the same from an electron beam. The cavity is defined by a box-like housing 36 having openings 37 and 38 in opposite walls through which the electron beams travel. Within housing 36 and disposed along and parallel to the opposite sides of the beam between the openings is a drift tube 39 which terminates short of each of the openings to define a pair of gaps 40 and 41. The coupler is constructed so that the gaps are fed in phase with the signal energy and are spaced in this instance to enhance the fast wave while cancelling the slow wave on the beam at the signal frequency.

As explained, the primary signal carrying beam in the apparatus shown in FIGURE 1 conveys cyclotron signal waves and therefore is a transverse mode device. The device illustrated in FIGURE 2 is of the other or longitudinal-mode class. A primary signal carrying electron beam is developed by an electron gun and projected along a primary beam path 46 until finally intercepted by a collector 47 connected to a suitable potential source B+. Signal energy from a source 48 to be amplified is impressed upon the beam by an electron coupler 49. Subsequently, amplified input signal energy is extracted by an output coupler 50 and delivered to a load 51. In a manner similar to that above discussed, the signal energy developed upon the primary electron beam, which in this cas is in the form of space-charge waves, is parametrically amplified under the influence of a field produced by a space-charge wave carried by a second or additional electron beam traversing adjacent beam path 53. This additional beam is developed and projected from electron gun 54 through a pump signal cupler 55 coupled to a pump source 56 and terminated by a resistor 57. The electron beams are confined throughout their travel so as to be of uniform thickness. In this case, the radius of the beams are maintained constant by a magnetic focusing field schematically labelled by the arrow H. Other known means for confining an electron beam may be employed, but it is most convenient in the present case to obtain the focusing field from a solenoid encircling the whole length of the tube and energized by direct current.

It is desired for low noise amplification to interchange noise and signal energy in coupler 49. One method of properly adjusting the coupler when fast and slow wave velocities are separated is by means of the known Kompfner-Dip technique. To apply this technique, a signal is applied from source 48 and a receiver is inserted between the other end of helix and ground, across the terminating resistor 58. The beam current and voltage are adjusted so that a null exists across the resistor. Under this condition, the beam noise is dissipated in the resistor while the signal noise on the helix of the coupler reaches a null. Thus, all signal energy flows from the source into the beam and the fast wave beam noise is transferred to resistor 58. Alternatively, the terminating resistor may be omitted and the extracted beam noise returned to the beam source which is matched to the helix.

In order that the coupler is designed to interact with the fast electron wave on the beam, helix 49 is constructed to have a propagation velocity u, in the absence of the electron beam which corresponds to the desired fast electron wave to be generated on the beam in operation. The same considerations are taken into account in constructing output coupler 50 and pump coupler 55. As with the coupler employed in the apparatus of FIG- URE 1, various beam interaction devices may be employed, including the double-gap coupler shown in FIGURE 10.

To understand the operation of the apparatus shown where 11 is the beam electron velocity and m is the input signal frequency. The resonant period of 'the resultant signal modulation is described by the plasma frequency which is a function of the DC. beam voltage and current density as more fully described in an article by G. M. Branch and T. G. Mihran entitled Plasma Frequency Reduction Factors in Electron Beams, appearing on volume ED-Z, No. 2 of the IRE Transactions on Electron Devices published under date of April 1955. As discussed in detail in that article, the effective or actual plasma frequency on the beam is reduced by various factors including fringing of the longitudinal electric field. The significant parameter as far as beam action itself is concerned is the reduced plasma frequency generally represented as w In the present instance the space-charge wave developed in response to signal energy from source 48 at a frequency o has a propagation constant and a reduced plasma frequency The driving-signal wave at frequency m is generated externally to the primary beam on the additional beam. Energy from this external driving-signal Wave is delivered to the space-charge wave on the primary beam to generate thereon an idler space-charge wave at a frequency o equal to w w with a corresponding reduced plasma frequency w g and having a propagation constant 5 which may for a fast idler wave be expressed as:

While 5 is equal to fl -l-fl it is unequal to the propagation constant [3 of any space-charge wave generated on primary beam 46 corresponding to the driving-signal frequency. 13 may be expressed as:

1 w -w I Bo Ue 3 (13) In consequence, the presence of any space-charge wave on beam 46 having propagation constant 5 is minimized. By utilizing a wave propagating beam external to the .primary beam but in coupling relation therewith and satisfying the conditions set forth, a driving signal wave is established which meets precisely the requirements for optimum signal amplification in the expander, while the magnitude of any space charge wave on beam 46 corresponding to the driving signal frequency is minimized. In consequence, the amplification process is both efiicient and cleanly defined, there being a minimum of undesired interaction productive of distortion by reason of the generation of harmonics and other spurious signals which would otherwise be produced if a space-charge wave of substantial energy corresponding to the driving signal frequency were permitted to exist on beam 46, as where 'URE 1 is shown in FIGURES 3, 3a.

a wave of such character is utilized to obtain the entire amplification action.

In the present apparatus, waves propagate on beam 53 with a propagation velocity 1% for signals at the driving frequency m which satisfies the expression:

It may even be made slightly greater than that to minimize undesired interaction with a space-charge wave at the driving frequency on beam 46. At the same time, the additional beam preferably has a propagation velocity for signals at the input frequency m which is substantially different from the propagation velocity of the input signal space-charge wave on the primary beam to avoid the development on beam 53 of a wave derived from the input-signal modulation capable of interacting with the desired primary beam wave.

While the prescribed relationships may be obtained in various ways, it is desired to enforce the desired conditions by making the primary beam comparatively thick. The word thick is understood in the art to establish a beam characteristic which serves to contrast with the thin beam often employed especially in longitudinalfield traveling-wave devices. A figure of quality may be established which sets forth the relationship between the circumference of the primary beam 211 and the electron wave length corresponding to the input signal on the beam, f being the input signal frequency and r being the beam radius. The ratio of the beam circumference to this electronic wave-length yields the figure of quality:

which equals wt T67" and which is conveniently expressed as [3617, where [3 is the electronic wave number corresponding to the frequency 6 In general, beam 46 may be considered thick when the figure of quality in consistent units exceeds approximately one-half. Other than circular beams may of course be employed and an equivalent figure of quality utilized. For example, with a sheet-like beam, the halfthickness instead of the radius of the beam is specified, the radius merely being the half-thickness of a generally round beam. A large figure of quality results in an increase of the difference between w on one hand, and the sum of w +w on the other; with the illustrative apparatus, w g is less than w +w Thus, a thicker primary beam brings about a greater separation between the propagation constant B of the undesired space-charge wave on the primary beam at frequency :0 and the propagation constant [3 of the externally applied driving-signal wave on beam 53.

An alternative to the apparatus illustrated in FIG- In this instance, the four pumping beams are replaced by a single hollow electron beam projected from an electron gun 60 along a path 60a so as to coaxially encircle the primary beam path 11. The primary electron beam may be developed from electron gun 10 and projected through an input coupler 13, an output coupler 18 and then intercepted by collector 12 in a manner essentially the same as that described for the FIGURE 1 apparatus. Operation of the input and output couplers is the same as that described in connection with FIGURE 1.

Electron gun 60 may be of any suitable construction and in this case includes a Pierce type gun having an annular cathode 61 and an apertured field forming structure 62 which together with successive annularly apertured electrodes 63, 64 develop and shape the hollow beam. For convenience, electron gun 10 may be disposed between electrodes 63 and 64 so as to project the signalcarrying or primary electron beam from an aperture centrally disposed in electrode 64.

In accordance with a principal feature of the FIG- URE 3 apparatus, the hollow pumping beam projected from electron gun 60 is modulated at different circumferential spaced azimuthal positions with the energy from the pump signal source. To this end, helices 66 preferably are disposed symmetrically around the surface of the hollow beam immediately adjacent thereto. Helices 66 are driven from a pump source in the same manner as illustrated in FIGURE 1 with respect to pump source 30. As shown primarily for convenience of illustration, helices 66 are shielded from beam path 11 by a drift tube 32 spaced on beam path 11 just beyond the input coupler. In this case, the parametric expansion process takes place between the downstream end of tube 67 and output coupler 18. As explained with respect to FIG- URE 1, it usually is preferred to dispose helices 66 directly adjacent input coupler 13 so that the entire space between the input and output couplers is used for parametric expansion.

In operation of the device shown in FIGURE 3, the

cyclotron wave, developed on the primary beam projected along path 11 under the influence of magnetic field H and the input signal impressed upon coupler 13, is subjected to the inhomogeneous time variable composite field developed by the individual signal waves propagating along the hollow pumping wave. Because of the presence of the magnetic field, the electrons in the hollow beam and the beam itself are effectively rotating about beam path 11 as the beam electrons progress therealong. Consequently, the individual pump signal waves developed by helices 66 follow helical orbits as a result of which the electrons in the primary signal beam on path 11 appear to see a pump signal field at a frequency different from that actually developed by the pump source. Accordingly, the pump signal frequency is varied from that which would be the case with pumping fields which propagate along paths parallel to beam path 11 as in FIGURE 1.

For the basic degenerative mode of operation, the cyclotron frequency is equal to the input signal frequency and the pump signal frequency is twice the cyclotron frequency. As stated, in the device of FIG- URE 3 the actual pump signal frequency differs from this value although the actual effect of the pumping field upon the signal carrying electrons is as if the second harmonic frequency relationship in fact exists. device may also be operated in the non-degenerative mode in which case the signal frequency may differ from the cyclotron frequency. For this mode of operation, the input and output couplers along beam path 11 may be constructed to exhibit a finite phase velocity selected to that the sum of the input, idler, and pump signal propagation constants is equal to zero.

Apparatus constructed in accordance with the present invention is especially suitable for the amplification of signals at extremely high frequencies. The pumping fields developed on the separate, additional pumping beams are capable of strongly influencing the primary beam waves as a result of which spacings may be employed which are of practicable value. In addition, by employing waves actually carried by electron streams to develop the necessary pumping fields, wall-charge and other effects encountered at high frequencies with circuit elements are avoided. It will be apparent that many variations of actual physical structure are possible with- The 8 out departing from the principles of operation herein discussed.

Accordingly, while particular embodiments of the invention have been shown and described, it will be obvious to those skilled in the art that changes and modifications may be made without departing from the invention in its broader aspects, and, therefore, the aim in the appended claims is to cover all such changes and modification as fall within the true spirit and scope of the invention.

I claim:

1. A parametric amplifier comprising: means for projecting a first electron beam along a first path; means for establishing electron resonance for electrons in said beam; input coupler means for developing on said beam a wave corresponding to input signal energy at a predetermined frequency and with a predetermined propagation constant; means for projecting at least one additional electron beam along a second path disposed in field coupling relationship with said first beam; means for developing on said additional beam a pump signal wave, having a frequency equal to the sum of said predetermined frequency and the frequency of the idler wave produced by the parametric process with the sum of said predetermined propagation constant and the propagation constants of said pump signal wave and said idler wave being equal to zero, to subject said electrons in said first beam to a time variable periodic inhomogeneous field having a phase relationship with said first-beam wave to deliver energy to a component thereof in proportion to the amplitude of said component; and means for extracting amplified signal energy from said first electron beam.

2. A parametric amplifier comprising: means for projecting a first electron beam along a first path; means for establishing cyclotron resonance for electrons in said beam; input coupler means for developing on said beam at transverse-mode wave corresponding to input signal energy at a predetermined frequency and with a predetermined propagation constant; means for projecting at least one additional electron beam along a second path disposed in field coupling relationship with said first beam; means for developing on said additional beam a pump signal space-charge wave, having a frequency equal to the sum of said predetermined frequency and the frequency of said idler wave produced by the parametric process with the sum of said predetermined propagation constant and the propagation constants of said pump signal wave and said idler wave being equal to zero, to subject said electrons in said first beam to a time variable periodic inhomogeneous field having a phase relationship with said first-beam wave to deliver energy to a component thereof in proportion to'the amplitude of said component; and means for extracting amplified signal energy from said first electron beam.

3. A parametric amplifier comprising: means for projecting a first electron beam along a first path; means for establishing space-charge resonance for electrons in said beam; input coupler means for developing on said beam a space-charge wave corresponding to input signal energy at a predetermined frequency and with a predetermined propagation constant; means for projecting at least one additional electron beam along a second path disposed in field coupling relationship with said first beam; means for developing on said additional beam a space-charge pump signal wave, having a frequency equal to the sum of said predetermined frequency and the frequency of the idler wave produced by the parametric process and a prop tion constant equal to the sum of the propagation constant of said idler wave and said predetermined propagation constant, to subject said electrons in said first beam to a time variable periodic inhomogeneous field having a phase relationship with said first-beam wave to deliver energy to a component thereof in proportion to the amplitude of said component; and means for extracting amplified signal energy from said first electron beam.

4. A parametric amplifier comprising: means for projecting a first electron beam along a first path; means for establishing space-charge resonance for electrons in said beam; input coupler means for developing on said beam a space-charge Wave corresponding to input-signal energy at a predetermined frequency; means for projecting at least one additional electron beam along a second path disposed in field coupling relationship with said first beam; means for developing on said additiontal beam a pump signal Wave at a frequency different from said predetermined frequency, but equal to the sum or" the latter and the frequency of the idler wave produced by the parametric process, said pump signal wave being coupled to said space-charge Wave to deliver energy thereto and having a propagation constant unequal to the propagation constant of any space-charge Wave produced on said first beam corresponding to said pump signal frequency but equal to the sum of the propagation constants of the input signal wave and the idler wave; and means for extracting amplified signal energy from said first electron beam.

5. A parametric amplifier comprising: means for projecting a first electron beam along a first path; means for establishing space-charge resonance for electrons in said beam; input coupler means for developing on said beam a space-charge wave having a propagation constant and a reduced plasma frequency o corresponding to signal energy at a frequency o means for projecting at least one additional electron beam along a second path disposed in field coupling relationship With said first beam; means for developing on said additional beam a pump signal space-charge Wave at a reduced plasma frequency w corresponding to a pump signal frequency o said pump Wave being coupled to said input-signal wave to generate on said first beam an idler space charge wave at a frequency m equal to w3wl, with a corresponding reduced plasma frequency w g and having a propagation constant [3 and said pump wave having a propagation constant B equal to [3 -1-3 with any space-charge wave on said first beam corresponding to the driving-signal frequency having a reduced plasma frequency smaller than the sum w +w so that the propagation constant of any such space charge wave cannot equal B and means for extracting amplified signal energy from said first electron beam.

6. A parametric amplifier comprising: means for projecting a first electron beam along a first path; means for establishing electron resonance for electrons in said beam; input coupler means for developing on said beam a wave corresponding to input signal energy at a predetermined frequency and with a predetermined propagation constant; means for projecting four additional electron beams along individual paths disposed in field coupling relationship with said first beam and spaced circumferentially around said first path; means for developing on each of said additional beams a pump signal wave, having a frequency equal to the sum of said predetermined frequency and the frequency of the idler wave produced by the parametric process with the sum of said predetermined propagation constant and the propagation constants of said pump wave and said idler wave being equal to zero, to subject said electrons in said first beam to a time variable periodic in homogeneous field having a phase relationship with said first-beam wave to deliver energy to a component thereof in proportion to the amplitude of said component; and means for extracting amplified signal energy from said first electron beam.

7. A parametric amplifier comprising: means for projecting a first electron beam along a first path; means for establishing electron resonance for electrons in said beam; input coupler means for developing on said beam a Wave corresponding to input signal energy at a predetermined frequency and with a predetermined propagation constant; means for projecting a hollow electron beam along a path coaxial with said first path and in field coupling relationship with said first beam; means for modulating said hollow beam at a plurality of circumferentially spaced positions thereof to develop a corresponding plurality of pump signal Waves, each having a frequency equal to the sum of said predetermined frequency and the frequency of the idler produced by the parametric process with the sum of said predetermined propagation constant and the propagation constants of said pump signal wave and said idler wave being equal to zero, to subject said electrons in said first beam to a time variable periodic inhomogeneous field having a phase relationship with said first-beam wave to deliver energy to a component thereof in proportion to the amplitude of said component; and means for extracting amplified signal energy from said first electron beam.

8. A parametric amplifier comprising: means for projecting a first electron beam along a first path; means for establishing electron resonance for electrons in said beam; input coupler means for developing on said beam a wave corresponding to input signal energy at a predetermined frequency and with a predetermined propagation constant; means for projecting four additional electron beams along individual paths disposed in field coupling relationship with said first beam and spaced circumferentially around said first path; means for developing on each of said additional beams a pump signal Wave, having a frequency equal to the sum of said predetermined frequency and the frequency of said idler wave produced by the parametric process with the sum of said predetermined propagation constant and the propagation constants of said pump signal wave and said idler signal wave being equal to zero, to subject said electrons in said first beam to a time variable periodic inhomogeneous field having a phase relationship With said first-beam wave to deliver energy to a component thereof in proportion to the amplitude of said component, the two pairs of oppositely disposed pump signal waves developing fields acting in phase opposition to generate a composite time-varying quadrupole field; and means for extracting amplified signal energy from said first electron beam.

References Cited in the file of this patent FOREIGN PATENTS 1,241,493 France Aug. 8, 1960 

1. A PARAMETRIC AMPLIFIER COMPRISING: MEANS FOR PROJECTING A FIRST ELECTRON BEAM ALONG A FIRST PATH; MEANS FOR ESTABLISHING ELECTRON RESONANCE FOR ELECTRONS IN SAID BEAM; INPUT COUPLER MEANS FOR DEVELOPING ON SAID BEAM A WAVE CORRESPONDING TO INPUT SIGNAL ENERGY AT A PREDETERMINED FREQUENCY AND WITH A PREDETERMINED PROPAGATION CONSTANT; MEANS FOR PROJECTING AT LEAST ONE ADDITIONAL ELECTRON BEAM ALONG A SECOND PATH DISPOSED IN FIELD COUPLING RELATIONSHIP WITH SAID FIRST BEAM; MEANS FOR DEVELOPING ON SAID ADDITIONAL BEAM A PUMP SIGNAL WAVE, HAVING A FREQUENCY EQUAL TO THE SUM OF SAID PREDETERMINED FREQUENCY AND THE 